1. Field of the Invention
The disclosure relates to a phosphor, and in particular relates to a white light emitting device utilizing the same.
2. Description of the Related Art
Use of white light emitting diodes is a major trend in modern illumination due to the energy-saving, low pollution, and long lifetime thereof. The critical points for total luminous efficiency in the illumination devices are not only the inherent brightness of LEDs but also the LED phosphors used.
The general commercially available white light LED is a blue LED (emission wavelength of 460 nm to 480 nm) collocated with a yellow phosphor, which has poor color-rendering due to the lack of red light. In other words, a white light LED utilizing a combination of red and yellow phosphors have better color rendering than the white light LED only utilizing the yellow phosphor. However, the major commercially available blue light excitable red phosphors are nitrides or sulfides, which have an emission wavelength of 620 nm to 650 nm. The red phosphors of nitride have high stability, but need expensive starting materials (e.g. strontium nitride and barium nitride) and expensive processes (e.g. high temperature and high pressure) for fabrication thereof. The cost of the red phosphor of sulfide is low, but it is not suitable for application in LEDs due to low chemical stability thereof. Recently, an orange red phosphor of silicate has been used to collocate with a yellow phosphor and blue LED to complete a white light LED with high color rendering. The usual orange red phosphor of silicate is (CaSr)2SiO4:Eu2+ (BOS600) and has an emission spectrum of 580 nm to 600 nm, a relatively low cost, good illumination efficiency, and better chemical stability than the red phosphor of sulfide. However, the thermal stability of BOS600 is not sufficient. Accordingly, an orange red phosphor having good illumination efficiency, a low cost, and excellent thermal stability is called-for.